a small parasitic catfish native to the amazon, that typically feeds off the blood of other fish. However is attracted to urine and has been known to swim up the vagina/penis/anus of nude bathers in the amazon river. Once inside a human host it extends spines on its back lodging it firmly in place where removal is possible through extremly painful surgery, amputation of the organ or the use of herbal medicines that can dissolve the parasite.

I'm never pissing in the Amazon cuz I don't want a candiru to swim up my urethra.